An Evolved Packet System (EPS) of 3GPP is composed of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW) and a Home Subscriber Server (HSS).
An EPS supports intercommunication with a non-3GPP system (as shown in FIG. 1). The intercommunication between the EPS and the non-3GPP system is implemented through an S2a/b/c interface, and a P-GW serves as an anchor between a 3GPP system and the non-3GPP system. In an EPS system architecture diagram, access of a non-3GPP system is divided into non-trusted non-3GPP access and trusted non-3GPP access. The non-trusted non-3GPP access needs to be performed through connecting an Evolved Packet Data Gateway (ePDG) and a P-GW. An interface between the ePDG and the P-GW is an S2b interface. Trusted non-3GPP access needs to be performed through connecting an S2a interface and a P-GW. The S2a interface performs information interaction by means of a Proxy Mobile Internet Protocol (PMIP). In addition, an S2c interface provides user plane-related control and mobility support between a User Equipment (UE) and the P-GW. A mobility management protocol supported by the S2c interface is Mobile IPv6 Support for Dual Stack Hosts and Routers (DSMIPv6), which is applicable to non-trusted non-3GPP access and trusted non-3GPP access.
A Wireless Local Area Network (WLAN) may function as an Evolved Packet Core (EPC) of a non-3GPP system, and may support the above three interfaces including the S2a, S2b and S2c interfaces. At current, there are lots of studies about processes and policy routing of the S2b and S2c interfaces.
As such a method as using a WLAN as a trusted non-3GPP system to access an EPC is gradually accepted by operators, the problems of process refinement and policy routing of the S2a interface start to be studied. Firstly, methods for triggering establishment of an S2a session without enhancing functions of an existing UE have been studied. As shown in FIG. 2, after a UE completes a non-3GPP-specific process and an Extensible Authentication Protocol (EAP) authentication process, an L3 message is carried out between the UE and a network element of a Trusted Non-3GPP IP Access Network (TNAN). After receiving the L3 message, the TNAN initiates an S2a session establishment process to a P-GW of a mobile core network. Besides the L3 message, an L2 message may also function as a triggering mode, such as an EAP message. The above methods for triggering establishment of an S2a session have been discussed and substantially accepted.
Currently, a UE does not support transfer of information including an Access Point Name (APN) and a Packet Data Network (PDN) type. However, these information is key information required by a 3GPP EPC to establish an S2a session or to allocate an IP address to the UE. For example, if APN information cannot be acquired, an extra PDN connection cannot be established for the UE. If a PDN type cannot be acquired, a P-GW cannot sense an IP address type requested by the UE and can only allocate an IP address according to a subscribed IP address type of the UE, but such an allocation method easily causes waste of IP address resources. In addition, when 3GPP access is switched to non-3GPP access, a UE fails to transmit, to an EPC, information in which the IP address of the UE needs to be reserved, thus failing to ensure service continuity.